Furnace and method of operating the same



July 12,-e 1932. H. P. KlRcl-HNER 1,867,012

FURNACE AND METIHOD 0F OPERATING THE SAME Filed July 21, 1930ssneets-sheet `1` I l flNVEN'lTOR July l2, 1932. H. P. KIRCHNER1,367,012

FURNAGE AND METHOD OF OPERATING THE SAME Filed July 2l, 1930 5Sheets-Shea?I 2 s M 1v n s .s /v

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FURNACE AND METHOD 0F OPERATING THE SAME l Filed July 21, 1930 3Sheets-Sheet 3 V Y/f y;

N lk 7'QINVEINTQR Patented July 12, 1932 e. mm1-:Dl STATE-s PATENTo1-FICE HENRY P. KIRCHNER, OF NIAGARA FALLS, NEW YORK, ASSIGNOR T THECARBORUN- I DUM COMPANY,

VANIA OF NIAGARA FALLS, NEW YORK, A CORPORATION 0F PENNSYL- FURNAGE ANDMETHOD OF OPRATING THESAME .Application led ll'uly- 21, 1930. Serial No.469,494.

6 perature and slagging conditions. The'n'- vention has specialapplication to the burning of powdered coal as a fuel in boiler furnacesbecause of the severity of the condioutside of the wall.

tions imposed upon the refractory forming the combustion chamber, but it1s not limite to such installations,

In the operation of boilers uslng powdered coal as a fuel, 4it is thepractice to run the boilers at several .hundred percent of theirordinary or normal rating. The limit at which the-boilers may be run isdetermined to a very large extent on the ability of the refractory tostand up for any-appreciable length of time at the high temperaturesemployed .and'under the destructive action of the slag. The rate ofcombustion in restrict-` ed portions of the combustion chamber may reach100,000 B. t. u.s. per cubicfootperhour.

This means temperatures of the o'rder of magnitude of 2700 degrees F. insuch com-f bustion regions. The heating of the walls'of the combustionchamber is`correspond1ngly severe. In such .cases fire-clay walls whichare subjected to the fluxing action'of the slag in the neighborhood ofsuch' intense combustion are rapidly disintegrated. y,

Fire-clay is a relatively poor conductor of heat. Consequently, there isno way 1n which the high temperature existing at the exposed face of thewall ,canv be redu'cedby the dissipation of heat through the wallitsilicon carbid as'a refractory for this type of furnace. iliconcarbide is three times as strong as {ire-clay at. these high tempera-4ing fire-clay wall. Y vtimes more thermally conductive than fireturesand is from six to nine times more thermally conductive. having the samemechanical stability can be This means that a wall about one-third thethickness of a correspond- If the material' is nine clay, heat maybedissipated through the wall twenty-seven times faster than it canthrough a v{ire-clay wall of equal mechanical stability at operatingtemperatures. The heat conducted through the walls is carried away by acurrentof air circulated against the unexposed face of the wall. Due tothe high conductivity of the "silicon carbide refractory wall the rateof cooling can be made. directly responsive to the change in thevelocity of the aircirculating against the wall. The air so used can bereturned to the combustion chamber to support combustion in the furnace,thus increasing the rate Aof combustion and preventing a needlesswasteof heat. By' circulating a sufficient volume .of cold air against theunexposed'face of the silicon carbide' wall it is possible to 4cool theexposed face of the refractory to a pointvwhere the-slag immediately incontact with the face f the wall congeals, forminga thin 'protectingskin "or-film y Vao Congealed slag has a lower thermal 'coni' ductivitythan silicon carbide. It has beenv further possible, by 'reason of thearrangement above described, to obtain acondition in 'which siliconcarbide bricks can be cooled suiicient'ly by internalcooling of the Wallto keep the exposed face ofthe wall covered -w'ith 'a llayerfofcongeale'd, slag about onequarter vof an inch thick,I A temperaturegradientl is established' through'the furnace Wall in which the rateof-fall of temperature is more rapid in passing'through the congealedslag film than in passing through the silicon carbide itself. f' Thismethod of operation is'described and claimed in a copending applicationofl C; E. Hawke, Serial No. 244,734,1iled January 5, 1928. Thisapplieation has become U. S. Patent 1,833,677.

This method of operation is su ject, how? ever, to. certain limitations.One of these is that the cooling action of the air diminishes n with theincrease in the temperature of the wipes the silicon carbide wall andabsorbs heat therefrom wipes against the water pipes and imparts heatthereto. The air is thus cooled to a considerable extent. This isdisclosed in a copending application of R. C. Benner, `Serial No.239,724, filed December 13, 1927. This application has become U. S.Patent #1,786,593.

- However, in the operation of furnaces, and

particularly powdered coal furnaces, thereis j a considerable change inthe temperature of the walls when the output of the boiler is changed.Changes of boiler rating are the main cause (but not' necessarily theonly cause) of changes of wall. temperature. These changes result in theproduction of areas over the 'furnace wall which are substantiallyhotter than other areas. Inasmuch as the maintenance of the siliconcarbide at these high temperatures in an intensely oxidizing atmosphereand in the 'presence of highly reactiveslags is dependentupon themaintenance of the congealedcoatin of slag, -itA is evident that (as aconsequence o the production of a hot area where the slag does not vcongeal or where the temperature of the ex- -posed face rises above thcongealing point) the refractory will lose its exposed to destruction.

According to the present invention I provide a method-of correcting thisdondition protection and be by selectively cooling different portions ofthe wall to a greater extent than other portions according to the'requirements of a particular area. I provide a furnace wherein thetemperatures ofdiiferent areas may bc determined, andprovide a furnacewherein different individual areas are susceptible of selective coolingto a greater or lesser extent.

The invention maybe readily understood by reference to the accompanyingdrawings in which:

Figure 1 is a more orlessdiagrammatic view of a steam boilerinstallation having a powdered coal burner, the view representing avertical section through the installation;

fFigure 2 is a more or less diagrammatic view showing a fragmentaryhorizontal section of a portion of a wall of the combustion chamber; v lA Figure 3., is a diagrammatic view of a meter board of the type whichmay be 'conveniently used in the system;

Figure 4 is a front view of the signal board with which the meter boardcooperates; and

Figure 5 shows a type of automatic regulator which may be employed withthe method.

Referring to the drawings, a pulverizing fan v2 feeds coal from a hopper3 through a feeder pipe 4 into the combustion space of a furnace,designated. generally as 5. The boilers are outlined at 6. The interiorof the combustion chamber 5 is lined with a refractory material having acoeicient of thermal conductivity which is relatively high as l lcompared with {ire-clay, and which is in excess of 0.006 cal/cm/sec/C.The lining,

designated generally as 8, may be made, forI example, of bonded siliconcarbide. The thermal conductivity of this material is from six tonine-times that of fire-clay. Surrounding the inner wall 8 and in spacedrelation thereto is an outer wall 9, the shell 9 preferably being offire-clay or `other insulating refractory. Between the walls 8 and 9 isan air circulating passage 7. Air is supplied to the space .7 by a fan11 which forces air through a pipe 12 into the space 7 through a port13. The air which is forced or circulated through the space 7 isdischarged through a pipe 14 which communicates with a chamber 15surrounding the turbulent burner 16. The pipe 4 terminates at theturbulent burner 16. The arrangement is' such that air which is forcedthrough the s ace 7 between the silicon carbide wall 8 an the outershell ofthe furnace-is discharged with the fuel into the combustionchamber. The primary air enters along with the coal through the feederpipe 4, and the secondary air comes in through chamber 15. A push rod17is used for varying the position of the baie or reiector 16 in such away that the shape of the fiame can be altered.

At various points about the` wall 8 and in different parts of thecombustion chamber are thermocouples so arranged that the junctions liein the conducting refractory close to the exposed surface thereof. Thesethermocouples, which are diagrammatically illustrated, are designated20.. As shown in Fig. 2, separate lead wires go from the thermocouplesto conveniently located indicators These may comprise a series ofmeters, as shown in Fig. 3. These meters, which constitute a form ofDArsonval galvanometer, are indicated as having a suspended armature Acarrying a mirror M located between poles S and N of a permanentunagnet.As well 'understoodby those skilled in the art, this type kof meter isvery sensitive tosmall 3 is a signal ly a protecting coating temperaturechanges. A separate meter is provided for each thermocouple in thefurnace wall.

Cooperatin with the meter board of Fig. ioard, as shown'inFig. 4, thesignal board being designated generally as 21. It is provided with aplurality of windows 22, each of which is divided into three areas ofdifferently colored glass. The first marked W is clear, the next markedY is yellow, and

the third marked R is red. Beams of light4 reflected from the mirrors Mof the several meters fall on the correspondingly positioned windows.The beam of. light, under normal operating conditions falls on thesections W of the respective windows, but as the furnace wall fora giventhermocouple becomes more highly heated than desired, the

mirror M of the galvanometer connected to the thermocouple in thatparticular section rotates, reflecting the beam first onto the Y areaand then onto the R area.

By reason ofthis arrangement the operator is enabled to know theapproximate temperature conditions under which each small area of thewall is operating. He can tell when any section of the wall is becomingdangerously overheated.

Located inthe furnace wall adjacent each thermocouple is an air inletpassage 23. This air inlet passage, opening into the space 7 adjacenteach thermocouple, is connected to a source of air supply, which may betheblower 11, or as shown in Figs. 1 and 2, it may be an auxiliaryblower 24. For this purpose I have shown a conduit leading from theblower 24 with branches extending to each of the connections 23. Eachconnection 23 is provided with its own individual valve 26. When athermocouple indicates to the operator that a given portion of the wallis getting too hot, the valve 26 in the air passage 23 most nearlylocated to that particular thermocouple is opened, allowing fresh coldair to enter that portion of the circulatin passage 7 and cool theportion of the wall ein overheated. The valve 23 is then adjusted to aposition which will maintain the desired temperature balance which keepscontinuousof slagon that particular part of the wall.

In the particular embodiment shown in Figs. 1 and 2 I have shown the fan11 with an adjustable damper 52 as constituting a means for forcing anormal current of air through` the passage-7. The fan 24 with its outletduct 25 and distributing passages 23 connected therewith constitute moreor less auxiliary air supply means. In each of the passages 23 y is anadjusting valve 26. It will be understood, however, that it is notnecessary to provide the fan 11, since all of the air for cooling may besupplied by the fan 24 which can be used to maintain the desired draftthrough the space' 7, the distribution of the entering air being changedfrom time to time by adjusting the valves 26 as may be necessary onaccount of change of boiler output and consequent change of temperaturedistribution in the furnace.

In the drawings I have shown water pipes 27 in the air circulating space7. These are connected at the top thereof to a common header 28, and atthe bottom to a common header 29. By means of valves 30 and 31 the ow ofwater or other cooling fluid through the pipes 27 may be controllad andthe direction of flow determined. The air in the passage 7, circulatingagainst thesepipes, transfers heat to the -water or other cooling fluidcontained therein, and thusrserves to cool the air. The watercirculation therefore dimlnishes the amount of air required in thecool-v ing of the furnaceto af-point where a greater proportion of theair used for cooling can also be used for combustion. This results in amore economical operation of the furnace.

In practicing the invention it is of course understood that a boilerfurnace using powdered coal fuel is under the operation of a skilledoperator. The operator, according to the signals indicated on the signalboard 21, selectively varies the distribution and circulation of air toand back of any particular wall section in accordance with therequirements of that section. In this way overheating of any portion ofthe wall can he varied, and as the hotter areas shift about due to thechanges in the boiler output (and consequently boiler rating) theoperator may selectively vary the degree of cooling obtained at any onepoint. This enables all-sections of the Wall to be operated at thetemperature desired and without overheating in any particular portion ofthe furnace. General conditions can betaken care of by varying theamount of air supplied by the fan 11 and through controlled 'circulationof fluid in the pipes or conduits 27. Localized conditions are takencare ofby 'means of the auxiliary g ducts 23 and theircontrol valves 26.

Through an arrangement of this kind it is possible to maintain acongealed coating of slag of the necessary thickness over differentindividual portions of the entire area notwithstanding the fact thatsome portions are heated more intensely than others and notwithstandingthe fact that there may be a shifting of the more intensely heatedportions from one area to another. By the use of the precautions I havedescribed even the hottest portion ofthe furnace wall may be kept be,

low the melting point of the fuel. ash under proper operating conditionsof the burner.4

If desired, automatic operation of the individual valves 26 may beemployed. One type of apparatus for doing this is disclosed in Fig. 5wherein the valve, corresponding to the valve 26, is designated 42,while the pipe corresponding to the conduit 23 is designated 43. v Athermocouple 40'is located in the wall 8 as previously described, andthe -leads from this thermocouple are connected to a relay 41. The relay41 is a temperature control unit such as is well known in the art andsuch as is used for reversing motors eml ployed to adjust valves i-nVentilating systems or water supply systems. The relay functions toconnect the lines L--L' or the lines H-H with current supply lines S-S.The lines L-L and H--H lead to a motor 44. The motorl 44 drives aneccentric 46 through a speed reducer 45.. The eccentric 46 operates abell crank lever 47. The lever 47 is connected through a link 48 with avalve operating extension 49. Upony .rocking the lever'47 in onedirection the valve42 is opened and upon moving it in the otherdirection the valve is closed. When the motor is energized through thelines L-L the motor operates in a direction to .close the valve 42 andwhen the motor is energized through the lines -H-H it is operated toopenfthe valve l pose of which is to close the circuit to the relay 41at predetermined time intervals only. It is not desirable that the motorshould operate too frequently, and the interrupter 50 permits itsoperation only at predetermined time intervals. When t-he interrupter isopen the motor cannot run and a certain equilibrium in the portion ofthe wall being controlled is effected., During this time that the motorcannot operate a definite temperature gradient inthe silicon carbidelining and slag coating may be reached and a continuous fluctuating ofthe valve first one way and then the other is avoided. If thetemperature at the thermal junction is too hot or too cold for theformation of a coating of slag of the desired thickness, this conditionis altered during the next closed period of the interrupter. I

I have not shown the wiring in detail, as itembodies merely the use ofwell-known electrical mechanism, and the details of the having kan aircooled silicon carbide wall, the steps which comprise circulating acurrent of air back of the exposed face of the-wall,A

cooling the air whereby the volume of air required is reduced andselectively applying additional air to different portions of the wallwhere the temperature conditions are .006 cal/cms/sec/cC., an outervlining of insulating -refractory paced fromsaid inner lining to form aspace r cooling air in motion, means for su ply ing the main body1 ofsuch air at a su cient rate to regulate t e temperature of the majorportion of the furnace wall, and additional means for supplyin coolinair to regulate the temperatures o selecte regions of the inner wall.

-`3. In a powdered coal furnace an inner wall consisting substantiallofsilicon carbide, an outer lining of insu ating refractory spaced fromsaid. inner lining to form a space for cooling air in motion, means forsu plying the main body of such air at a sufclent rate to regulate thetemperature of the major portion of the furnace Wall, andadditionalfmeans for supplying more cooling air to hotter individualareas of the inner lining, said additonal means being automaticallycontrolled in accordance with the temperatures of such individual areas.

f In testimony whereof I have hereunto set m hand.

y y I HENRY P. KIRCHNER.

motor control circuit are known to those skilled in the art.

While lI have shown and described certain specific embodiments of myinvention, it will be understood that this is merely by way ofillustration and that various changes and modifications in the detailsof construction` Y.

and arrangement o f parts may bemade 'withf

